Near-UV Reflective Structural Color via Layer-by-Layer Deposition

Applications

This technology has applications in the development of pigments to prevent photodegradation of polymer coatings. Additionally, these pigments can be used in architectural, automotive, and aerospace coatings to repel birds and insects.

Problem Addressed

Unprotected polymer surface coatings, including those made of otherwise durable materials like polyesters, undergo rapid degradation when exposed to light due to the effect of energetic photons with wavelengths in the near ultraviolet (NUV) region. Conventional strategies to extend the lifetime of these polymers involve the incorporation of inorganic UV absorbers such as carbon black and titanium dioxide. This has a detrimental effect on the cosmetic appearance of these polymers. The NUV-reflective coatings described in this invention allows the mitigation of polymer photodegradation with minimal impact on appearance.

Coincidentally, the NUV radiation responsible for photodegradation of polymers is also involved in animal communication. This allows the proposed NUV-reflective coatings to address a multitude of problems caused by animal collisions with buildings and aircraft by emitting animal-repelling NUV signals.

Technology

The NUV reflective coating described in this invention is fabricated by alternately depositing nanoparticle layers made of high refractive index material (e.g., TiO2) and low refractive index material (e.g., SiO2) using an aqueous layer-by-layer (LbL) assembly scheme. The refractive index of each layer is a function of its nanoporosity and can, therefore, be tuned by varying assembly conditions.

A TiO2/SiO2 multilayer functions as a Bragg mirror which selectively reflects light at multiple bands depending on the relative thickness of its constituent layers. The location and width of these reflectance peaks can be tuned to suit specific applications. For the particular application of NUV-reflective coatings, secondary reflectance peaks in the visible wavelengths may alter the visible color of the coating. The effect of these secondary peaks can be mitigated by adding a half, high refractive index stack to the main stack, resulting in a NUV-reflective coating with minimal visible color interference.

Advantages

  • Tunable multiband NUV reflection behavior
  • Minimal impact on cosmetic appearance of polymer coatings possible
  • Aqueous LbL assembly is environmentally friendly, low-cost, and compatible with complex surface geometries